A liquid crystal display (LCD) device is a display device that controls the alignment of birefringent liquid crystal molecules to control the transmission/shielding of light (on/off of display). Examples of display modes of LCD include a vertical alignment (VA) mode in which liquid crystal molecules having negative anisotropy of dielectric constant are aligned vertically to a substrate surface; an in-plane switching (IPS) mode and a fringe field switching (FES) mode, in which liquid crystal molecules having positive or negative anisotropy of dielectric constant are aligned horizontally to a substrate surface to apply a horizontal electric field to a liquid crystal layer.
Among these, in a multi-domain vertical alignment (MVA) mode in which liquid crystal molecules having negative anisotropy of dielectric constant are used and a rib or a slit of an electrode is provided as an alignment regulating structure, a liquid crystal alignment direction during voltage application can be controlled in plural directions without subjecting an alignment film to a rubbing treatment, and thus viewing angle characteristics are superior. However, in an MVA-LCD of the related art, an upper side of a rib or an upper side of a slit is the boundary of alignment division of liquid crystal molecules, the transmittance during white display is low, dark lines are observed in the display, and thus there is room for improvement.
In contrast, as a method for obtaining a high-luminance and high-speed response LCD, alignment stabilization techniques using a polymer (hereinafter, also referred to as “polymer sustained (PS) technique”) have been suggested (for example, refer to Patent Literatures 1 to 8). Among these, in pre-tilt angle imparting techniques using a polymer (hereinafter, also referred to as “polymer sustained alignment (PSA) technique”), polymerizable components such as polymerizable monomers and oligomers are mixed to obtain a liquid crystal composition; the liquid crystal composition is sealed between substrates; and the monomers are polymerized to form a polymer in a state where liquid crystal molecules are tilted by applying a voltage between the substrates. As a result, the liquid crystal molecules have a certain pre-tilt angle even after the voltage application is stopped, and thus the alignment direction of the liquid crystal molecules can be regulated to be uniform. The monomers are selected from materials which are polymerizable by heat, light (ultraviolet rays), or the like. In addition, the liquid crystal composition may contain a polymerization initiator for initiating the polymerization of monomers (for example, refer to Patent Literature 4).
Examples of other liquid crystal display elements using a polymerizable monomer include polymer dispersed liquid crystal (PDLC) and polymer network liquid crystal (PNLC) (for example, refer to Patent Literature 9). These elements include a polymer which is formed by adding a polymerizable monomer to liquid crystal and irradiating the mixture with ultraviolet rays or the like; and perform light scattering switching by using the matching and non-matching of refractive indices between the liquid crystal and the polymer. In addition, examples of the other liquid crystal display elements include polymer-stabilized ferroelectrics liquid crystal (FLC) phase (for example, refer to Patent Literature 10), and polymer-stabilized optically compensated bend (OCB) (for example, refer to Non Patent Literature 1).
Meanwhile, in recent years, as a technique for obtaining superior viewing angle characteristics, a photo-alignment technique is investigated in which the liquid crystal alignment direction during voltage application can be controlled in plural directions without subjecting an alignment film to a rubbing treatment and thus superior viewing angle characteristics can be obtained. The photo-alignment technique is a technique in which a photoactive material is used to form an alignment film; and the formed film is irradiated with light rays such as ultraviolet rays to impart an alignment regulating force to the alignment film (for example, refer to Patent Literature 11).
Furthermore, recently, when the photo-alignment technique is used in combination with the polymer stabilization techniques using a polymer, a research on a method of suppressing hysteresis has been disclosed (for example, refer to Non Patent Literatures 2 and 3). Non Patent Literatures 2 and 3 disclose a configuration of adjusting the concentration of a monomer which is mixed with liquid crystal in an IPS mode cell in which one substrate is subjected to a rubbing treatment and the other substrate is subjected to a photo-alignment treatment.